By distribution networks in this application are meant electric a.c. networks for distribution of electric power at voltages of up to about 50 kV. Normally, such networks are of three-phase design but the invention can also be applied to, for example, single-phase networks. The concept distribution network in this connection also includes networks for distribution of electric power for special purposes, for example for power supply of railway systems.
It is previously known to use series compensation in distribution networks, which, inter alia, gives the following advantages:
reduced line voltage drop PA1 reduction of the line losses PA1 reduced voltage variations PA1 increased transmission capacity PA1 increased power factor PA1 simplified start-up of large motors.
By series compensation of a highly loaded distribution line, a reconstruction can be avoided or postponed. The reduction of the line losses which is achieved by a series compensation can result in considerable savings of costs.
In series capacitor equipment of the kind referred to here, circuit breakers of outdoor type have been used for bypassing of the capacitor, which, on the one hand, entails a high price and, on the other hand, are normally installed on the ground, which requires the acquisition of ground and the provision of fences. Spark gaps have been used as overvoltage protective means. However, it is difficult to obtain a satisfactory function of these spark gaps at the low voltages which are used in distribution networks (e.g. difficult to avoid unjustified trippings), and, furthermore, they require extensive maintenance.
Therefore, for reasons of reliability and cost, series compensation equipment has only had limited use in distribution networks.